1. Field of the Invention
The invention relates to a control apparatus of an electromagnetic drive valve operating mechanism that opens and closes intake valves and exhaust valves used in an internal combustion engine through cooperation of electromagnetic force and elastic force.
2. Description of the Related Art
There exists an electromagnetic drive valve operating mechanism in which an armature is fixed to the stem of a valve, and each one of two opposite sides of the armature in the direction of an axis of the stem is provided with one electromagnet that is coaxial with the stem. In this mechanism, when the upper and lower electromagnets are in a non-driven state, the armature is positioned at a neutral position by upper and lower springs. By causing the armature to be attracted and attached to the upper-side electromagnet, the valve body is disposed at a fully closed position. Furthermore, by causing the armature to be attracted and attached to the lower-side electromagnet, the valve body is disposed at a fully open position (e.g., see Japanese Patent Application Publication No. JP-A-2002-266667, and Japanese Patent Application Publication No. JP-A-2001-193504).
As for the actions, by alternately controlling the supply and the stop of the exciting current with respect to the upper and lower electromagnets at a timing that is in accordance with the need, a movable portion that includes the armature and the valve body is displaced in the direction of the axis so that the valve is opened or closed.
In the case of an electromagnetic drive valve operating mechanism as described above, when the valve body is to be opened or closed, the supply of the hold current supplied to the electromagnet is stopped in order to separate the valve body attracted and attached to the electromagnet. However, since a time is needed between the stop of supply of the hold current and the disappearance of the residual electromagnetic force that remains in the electromagnet, a response delay (delay time) before the valve body actually begins to open or close occurs.
Therefore, this delay time is predicted, and a feed forward control is preformed in such a direction as to advance the command timing for starting the opening/closing action of the valve body. The predicted delay time is a fixed value that is empirically determined as a constant through experiments or the like.
In the foregoing electromagnetic drive valve operating mechanism, there are matters for improvement in the following respects.
That is, the residual electromagnetic force of each electromagnet used in the electromagnetic drive valve operating mechanism varies due to individual differences of the electromagnets used, so that the response delay may vary. This response delay may vary also depending on the operation situation (rotation speed, load, or the like) of an internal combustion engine. Therefore, if the predicted delay time for use in the feed forward control is a fixed value as in the above-described electromagnetic drive valve operating mechanism, it can be said that variations in the response delay cannot be absorbed.
Furthermore, to set fixed values as the predicted delay time, many actual delay times are measured in experiments. However, since the measurement end timing, that is, the position at which the valve body actually begins to open or finishes closing, cannot be accurately detected, it can be said that the predicted delay time cannot be accurately set.
The measurement end timing (timing at which the valve body actually begins to open or finishes closing) is judged on the basis of the output of a lift sensor. The timing at which the valve body actually begins to open is defined as a position of the valve body that is very slightly apart from the fully closed position, while the timing at which the valve body actually finishes closing is defined as a position of the valve body that is limitlessly adjacent to the fully closed position. Since there is a need to detect these positions by the output of the lift sensor, noise contamination of the output of the lift sensor, if any occurs, will make it extremely difficult to discriminate the lift position of a very small amount and noise.
Therefore, it can be said that the discrimination of the measurement end timing includes an error. If the fixed value as the predicted delay time is determined on the basis of a result of measurement with such a large error, it has to be said that the correctness of the fixed value is low.
Thus, since variations in individual differences of electromagnets cannot be absorbed and, furthermore, since the predicted delay time is set at a fixed value whose correctness is low, the possibility of the actual valve timing deviating from a target valve timing is considered to be high. Occurrence of such a deviation leads to torque fluctuations of the internal combustion engine, such as deviation of the combustion condition of the internal combustion engine from a proper range, etc., and is therefore not preferable.
It is conceivable that after the above-described feed forward control, a feedback control is performed in which an actual delay time is detected in association with the actual action of the valve body and a result of detection is used to correct the fixed value. However, if at the time of the detection, the measurement end timing of the actual valve body is set at the timing at which the valve body actually begins to open or finishes closing, it can be said that the correctness of a result of measurement of the actual delay time becomes low as in the foregoing case.